Anti-soiling coating for an ophthalmic lens

ABSTRACT

A hydrophobic and/or oleophobic coating system for an ophthalmic lens having increased effective thickness and water contact angle. In one embodiment, the hydrophobic and/or oleophobic coating system comprises an anti-reflective coating applied to an ophthalmic lens, the anti-reflective coating comprising alternating layers of high and low index materials with an outer layer of silicon dioxide having exposed hydroxyl groups. A hydrophobic coating is applied to the anti-reflective coating, the hydrophobic coating comprising a silane with a hydrophobic group and fewer than three reactive groups capable of bonding to the exposed hydroxyl groups of the anti-reflective coating.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/820,364, filed on Mar. 19, 2019, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to optical coatings for ophthalmic lensesand, in particular, to hydrophobic and/or oleophobic coating systems forophthalmic lenses.

Ophthalmic lenses are typically provided with one or more opticalcoatings that impart improvements to lens performance, such as scratchresistance, anti-reflection, anti-static, and other properties. A finalanti-soiling coating is often applied on top of these other coatings,which has hydrophobic and/or oleophobic properties to protect the innercoatings from moisture and to improve the ease of cleaning the surfaceof the lens. The hydrophobic and/or oleophobic coating also increasesthe durability of the lens coating system by providing a slick surfacefor foreign materials to slide off and avoid damage to the surface ofthe lens.

The hydrophobicity of the coating may be measured by the water contactangle of the surface of the coating—i.e. the angle formed between atangential line drawn at the point where the outer surface of a drop ofwater contacts the coating surface. For example, a perfectly sphericaldrop of water on a surface would rest at a single point on the surfaceand have a contact angle of 180°. Hydrophobic coatings generally have awater contact angle in excess of 90°. Hydrophobic coatings applied tosmooth surfaces can typically achieve water contact angles of up toabout 120°. Superhydrophobic surfaces with water contact angles greaterthan 150° can be achieved using rough surfaces that have micro/nanostructures.

Conventional hydrophobic coatings for ophthalmic lenses typically have amaximum water contact angle of about 112° to 113°, which falls wellshort of the potential maximum water contact angle of about 120° thathas been achieved for smooth surfaces. Thus, it would be desirable toprovide a hydrophobic coating that more closely approaches the maximumwater contact angle of 120°. The increase in hydrophobicity wouldsubstantially improve the anti-soiling properties of the coating, andthe protection and durability of the inner coating layers of theophthalmic lens.

SUMMARY OF THE INVENTION

Anti-soiling coating systems for ophthalmic lenses are disclosed,comprising an optical lens, a first coating applied to the lens thatcomprises an outer layer of silicon dioxide having exposed hydroxylgroups, and a hydrophobic second coating applied to the outer layer ofthe first coating. The second coating comprises a silane with afluorinated hydrocarbon group and that has either 1 or 2 functionalgroups that are reactive to form a bond with the exposed hydroxyl groupsof the first coating. In one embodiment, the first coating is ananti-reflective coating comprising alternating layers of high and lowindex materials. In a preferred embodiment, the layers of high indexmaterials are selected from the group consisting of: TiO₂, ZrO₂, andHfO₂, and the layers of low index materials are selected from the groupconsisting of: SiO₂, MgF₂, and Al₂O₃. In another embodiment, thefunctional groups are methoxy groups, and the silane preferably includesan ethoxy group. In another embodiment, the hydrophobic second coatinghas a water contact angle greater than 113°, preferably between 113° to114°, and more preferably between 115° to 117°. In another embodiment,the hydrophobic second coating forms a layer with a maximum effectivethickness that is greater than 20 nm, preferably at least about 30 nm,and more preferably at least about 40 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the chemical structure of an anti-soiling coating systemcomprising a conventional fluorinated silane, applied to a layer ofsilicon dioxide.

FIG. 2 shows the chemical structure of an embodiment of an anti-soilingcoating system comprising a fluorinated silane having two methoxy groupsand one ethoxy group, applied to a layer of silicon dioxide.

DETAILED DESCRIPTION OF THE INVENTION

Anti-soiling coatings systems for ophthalmic lenses are described.Ophthalmic lenses are commonly produced with multiple optical coatings.For example, a hard coating may be applied to the surface of the lens toincrease scratch resistance and durability. An anti-reflective coatingmay be applied on the scratch-resistant coating, to reduce reflectionsand glare from the surface of the lens. A hydrophobic and/or oleophobiccoating may be applied on the anti-reflective coating, to repel waterand oils, facilitate cleaning and protect the anti-reflective coating.

Typical hydrophobic coatings include fluorinated compounds, such asfluorinated siloxanes, fluorinated silanes, fluorinated silanols and/orfluorocarbons. Such fluorinated compounds may also be oleophobic inaddition to being hydrophobic. The hydrophobic coating may be applied tothe surface of the lens by a variety of means known in the art,including vacuum deposition. The hydrophobic coating bonds with or isotherwise strongly adhered to the underlying substrate and is resistantto mechanical removal, such that it is generally not removable by wipingwith solvents or similar mechanical means.

Not wishing to be bound by any particular theory, it is believed thatthe hydrophobic coating adheres to the substrate through chemical bonds.FIG. 1 shows an example of a hydrophobic coating system, comprising ahydrophobic compound applied to an anti-reflective coating substrate 10.The hydrophobic coating molecule 12 is a silane with a hydrophobicgroup, such as a fluorinated hydrocarbon (X). Conventionalanti-reflective coatings typically comprise alternating layers of highand low index materials. Common high index materials include metaloxides such as TiO₂, ZrO₂, HfO₂, and common low index materials includeSiO₂, MgF₂, Al₂O₃. In the embodiment of FIG. 1, the anti-reflectivecoating has an outer layer of silicon dioxide (SiO₂) with exposedhydroxyl (OH) groups. The hydrophobic coating adheres to theanti-reflective coating through hydrogen bonding and/or covalent bondingbetween the silanol groups of the fluorinated silane and the OH groupsof the silicon dioxide layer. Those of skill in the art will appreciatethat different substrates and hydrophobic coatings may involve differentchemical bonding interactions.

The water contact angle of the hydrophobic coating generally increasesas the thickness of the coating is increased. However, there is a pointat which the hydrophobicity of the coating peaks and remains essentiallyconstant despite the increasing thickness of the coating. Conventionalhydrophobic coatings typically achieve a maximum water contact angle ofabout 112° to 113° at a coating thickness of about 20 nm. At thisthickness, it is believed that the sites available on the substrate toreact and form chemical bonds with the hydrophobic coating areeffectively saturated, and that additional hydrophobic coating is onlyweakly adhered and is mechanically removable. Thus, conventionalhydrophobic coatings have a maximum effective thickness of about 20 nm,and the application of the hydrophobic material at a thickness greaterthan 20 nm does not appreciably increase the water contact angle of thehydrophobic coating.

Modification of the hydrophobic compound may allow an increased densityof hydrophobic compound molecules that are bonded to the substrate andincrease the maximum effective thickness of the hydrophobic coating.Conventional hydrophobic compounds have multiple functional groups thatare capable of reacting with and bonding to multiple sites on thesubstrate. For example, fluorinated silane hydrophobic compounds mayhave the general formula CF₃(CF₂)_(n)(CH₂)_(m)Si(OR)₃, where m≥0, n≥1and is preferably 2, 4 or 6, and R is preferably hydrogen or an alkylgroup, such as a methyl group. In the case where R is a hydrogen group,the fluorinated silane has three reactive groups capable of bonding tothe OH groups of the substrate, as shown in FIG. 1.

To increase the density of hydrophobic compound molecules bonded to thesurface of the substrate, one or more of the reactive functional groupsmay be substituted with a less reactive group. FIG. 2 shows anembodiment of a modified hydrophobic compound 14 that occupies fewerbinding sites on the substrate 10, which allows additional hydrophobiccompound molecules to bond to the substrate. Methoxysilanes can bond tothe OH groups of a substrate under anhydrous conditions at elevatedtemperature, whereas ethoxysilanes are less reactive and may requirecatalysis. Fluorinated silanes comprising a combination of methoxy andethoxy groups have a reduced number of functional groups (i.e. less thanthree, either 1 or 2) that are capable of readily reacting with andbonding to the OH groups of a silicon dioxide substrate, which allowsmore fluorinated silane molecules to bind to the substrate.

The increased density of hydrophobic compound molecules on the substrateis believed to permit thicker effective hydrophobic coatings withincreased water contact angles. Modified hydrophobic compounds withincreased maximum effective thickness are commercially available (KisanKinzoku Chemicals Co. Ltd., Japan), which comprise a fluorocarbon withreactive groups capable of bonding to the OH groups of a silicon dioxidelayer. Table 1 shows the coating thickness and resulting water contactangle for the modified hydrophobic compound.

TABLE 1 Hydrophobicity Coating Thickness Water Contact Angle 20 nm111°-112° 30 nm 113°-114° 40 nm 115°-117° 50 nm 115°-117° 60 nm115°-117°

The modified hydrophobic compound has a peak water contact angle of 117°at a maximum effective thickness of 40 nm. Thus, the modifiedhydrophobic compound can be effectively applied in at least twice thethickness of conventional hydrophobic compounds, which results in asubstantial increase in water contact angle and hydrophobicity that moreclosely approaches the potential maximum water contact angle of 120°.

Those of skill in the art will appreciate that the effective thicknessof the hydrophobic coating and the maximum water contact angle will varyas a function of the formulation and structure of the hydrophobiccompound. Furthermore, the invention is not limited in application toany particular type or form of lens, and may include finished orsemi-finished lenses made of any of the various materials known in theart. While particular embodiments of the present disclosure have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the present disclosure. It istherefore intended to cover in the appended claims all such changes andmodifications that are within the scope of this disclosure.

What is claimed is:
 1. An anti-soiling coating system for an ophthalmiclens, comprising: an optical lens; a first coating applied to the lens,comprising an outer layer of silicon dioxide having exposed hydroxylgroups; a hydrophobic second coating applied to the outer layer of thefirst coating, the second coating comprising a silane with a fluorinatedhydrocarbon group and having either 1 or 2 functional groups that arereactive to form a bond with the exposed hydroxyl groups of the firstcoating.
 2. The anti-soiling coating system of claim 1, wherein thefirst coating is an anti-reflective coating comprising alternatinglayers of high and low index materials.
 3. The anti-soiling coatingsystem of claim 2, wherein the layers of high index materials areselected from the group consisting of: TiO₂, ZrO₂, and HfO₂, and thelayers of low index materials are selected from the group consisting of:SiO₂, MgF₂, and Al₂O₃.
 4. The anti-soiling coating system of claim 1,wherein the functional groups are methoxy groups.
 5. The anti-soilingcoating system of claim 4, wherein the silane further has an ethoxygroup.
 6. The anti-soiling coating system of claim 1, wherein thehydrophobic second coating has a water contact angle greater than 113°.7. The anti-soiling coating system of claim 1, wherein the hydrophobicsecond coating has a water contact angle between 113° to 114°.
 8. Theanti-soiling coating system of claim 1, wherein the hydrophobic secondcoating has a water contact angle between 115° to 117°.
 9. Theanti-soiling coating system of claim 1, wherein the hydrophobic secondcoating forms a layer with a maximum effective thickness greater than 20nm.
 10. The anti-soiling coating system of claim 1, wherein thehydrophobic second coating forms a layer with a maximum effectivethickness that is at least about 30 nm.
 11. The anti-soiling coatingsystem of claim 1, wherein the hydrophobic second coating forms a layerwith a maximum effective thickness that is at least about 40 nm.